So what determines whether a player is popular or not.
Skill: If you don't have skill now or ever in the past, it doesn't what other characteristics you may posess.
+ Savior, iloveOov
Play Style: Are you interesting to watch or not? Do you do the same cookie-cutter macro builds or do you bring something exciting every game?
+ July, Nal_rA
- Justin, most terrans
Personality: Winning ceremonies, interviews, gossip. This can really go both ways, as some people may like and others will dislike certain personalities.
+/- Midas, Chalrenge, Zeus
Age: How well established a player is; how many years he's been around in the pro gaming circuit. Also, new Protoss players stand out much more than new Terran players
- Darkelf, 910, go.go, FreeDom, Sheis, Shine, etc.
Other factors that may also affect popularity, but generally not as applicable to all players
Bandwagon: A few incidents can be interpreted by a few respected forum members (read: blue names) to make judgments about a player, especially a new one. Also, for new members to TL, the consensus has generally been established already.
Screennames: Cool ones instantly win points, while lame ones are instantly made fun of. Taking your name after another progamer is also uncool. Also, changing your handle multiple times, especially to something stupid is looked down upon.
Looks: One way to win a lot of female fans at least.
+ Yellow, Xellos
[Edit: If you are looking for Reach, he has his own section below.]
Race: Personal preference. For me, that means Zerg.
Beating popular players: Especially for newer players that are only known because they beat everyone's favorites without ever playing spectacularly or anything.
Of course, no discussion of popularity would be complete without mentioning the two most popular players of all time, at least on TeamLiquid.
Boxer. He's always been near the top, extremely entertaining play, really modest and mature guy, been around forever, pioneered the game, the face of StarCraft progaming.
Reach. Definitely skilled (or at least used to be), manly play style, cool guy, been around for years, protoss user, very vocal fanbase, and very good looks.
[Edit: Don't get wrong me wrong though, he's awesome for more than just his looks]
I would say these two guys are two players that 99% of TL always roots for regardless of everything else (there's actually one exception for me: if their opponent is Savior )